The influence of isoniazid (INH) therapy on the effectiveness of intralesional BCG was studied in the guinea pig-hepatoma model of Rapp and Zbar, in which the intratumor injection of BCG is highly curative. INH, in the schedules and dosages that we used, did not interfere with the antitumor effect of intralesional BCG, although early INH therapy appeared to prolong the interval between intralesional BCG injection and clinical tumor cure. Six week old Balb/c mice were immunized with an allogeneic tumor and serially tested in a microcytotoxicity assay and in a Winn assay, in which immune serum, spleen cells, or peritoneal exudate cells were mixed with melanoma cells and injected into normal mice. The Winn assay appeared to give the results that were most consistent and intepretable. Vitamin A inhibits the growth and development of S-91 melanoma in Balb/c mice. The required dose for this effect is 3500 u/day for 5 days. Vitamin A treatment can be given after tumor inoculation. Vitamin A was effective in transiently slowing the appearance of tumor nodules in one experiment with a histocompatible melanoma. In one of two experiments with syngeneic MCA-sarcoma in Balb/c mice vitamin A delayed and slightly decreased tumor deaths. BIBLIOGRAPHIC REFERENCES: Felix, E.L., Loyd, B., and Cohen, M.H.: Inhibition of the growth and development of the transplantable murine melanoma by vitamin A. Science 189: 886-888, 1975. Felix, E.L., Cohen, M.H., and Lloyd, B.C.: Immune and toxic anti-tumor effects of systemic and intralesional vitamin A. J. Surg. Res. 21: 307-312, 1976.